A liquid crystal display device has been used as a display device for a computer. In recent years, such liquid crystal display device comes into increasing use for displaying a moving picture. This is because (i) use of the liquid crystal display device as a television has been developed as a result of development of a larger liquid crystal display device, and (ii) it becomes possible to process moving picture on computer as a result of improvement in performance thereof.
The liquid crystal display device has such characteristics that (i) it is free from screen flicker, (ii) it can have a thin thickness; (iii) it has low power consumption; (iv) and so on. Due to these characteristics, the liquid crystal display device has been attracting attentions as a device that applicable to a television and the like in replacement of prevailing CRT (Cathode-Ray Tube) display devices.
In the liquid crystal display device, a slow response speed becomes a big problem in displaying the moving picture on a liquid crystal module. More specifically, when the moving picture is displayed on the liquid crystal display device whose response speed is slow, after-image appear on the screen, thus causing ghosting of the moving picture. This causes deterioration in displaying quality. In the liquid crystal display device, the response speed from an intermediate graduation to an intermediate graduation is slower than response speed from black to white. Therefore the liquid crystal display device cannot display natural-color moving pictures without significant deterioration in display quality in some frames.
For example, Japanese Publication Examined Patent application Publication No. 25556/1988 (Tokukoushou 63-25556; published on May 25, 1988) discloses a method for improving the foregoing problem of the slow response speed of liquid crystal. The method disclosed in the above publication adopts a method called overshooting or overdriving. In these driving methods, a change greater than a change instructed in the input data is applied to a liquid crystal module, thereby improving the response speed.
In the liquid crystal display device, temperature within a liquid crystal panel is largely affected by environment temperature surrounding the liquid crystal panel. Further, during the display operation, various parts of the liquid crystal panel have various temperatures. Accordingly, in order to improve the response speed appropriately, it is necessary to apply to the liquid crystal panel such a change that is, to an extent required by the temperature within the liquid crystal panel, greater than the change instructed by the input data. if the response speed is not improved as such, deterioration in the displaying quality occurs while the moving picture is displayed.
In order to solve the foregoing problem, for example Japanese Patent No. 2507713 (issued on Jun. 19, 1996) discloses a liquid crystal display device conventionally including temperature sensors Th1 to Th8 mounted along edges of a liquid crystal panel 101 as shown in FIG. 16. By using these temperature sensors Th1 to Th8, temperature of the liquid crystal panel 101 is measured. Then, voltage impressed to anti-ferroelectric liquid crystal (AFLC) is changed in accordance with the measured temperature, so as to correct overall temperature-caused fluctuation in brightness of the liquid crystal panel 101.
More specifically, for example, changes in the temperature in the liquid crystal panel of the liquid crystal display device are compensated for by the following methods. Namely, in one of the methods, temperatures at edges of the liquid crystal panel 101 is measured, and an average temperature is calculated based on the temperatures measured. Then, the temperature of the liquid crystal panel 101 is estimated based on the average temperature, and pulse widths of scan voltage and signal voltage are changed in accordance with the temperature thus estimated, thereby causing response characteristic of the liquid crystal panel to correspond with the changes in the temperature. In another method, the liquid crystal liquid panel 101 is divided into four regions as shown in FIG. 17. Then the temperatures at the edges of the liquid crystal panel 101 are measured, and respective temperature distributions in the four regions are estimated based on the temperatures measured. Then, the pulse widths of the scan voltage and the signal voltage are changed in accordance with the temperature distributions thus estimated, thereby causing the response characteristic of the liquid crystal panel to correspond with the changes in the temperature.
As described, in the foregoing liquid crystal display device, the temperatures of a displaying surface of the liquid crystal panel 101 is estimated based on the temperatures measured at the edges of the liquid crystal panel 101. Then, respectively in accordance with the temperatures estimated, the correction is carried out in the four regions. This method, however, does no more than rough correction in response to the changes in the temperature by referring to the estimated temperature of the liquid crystal panel based on the temperatures at the edges of the liquid crystal panel. Therefore, even by the arrangement in which the liquid crystal panel is divided into the four regions, there still remains a problem that it is impossible to accurately compensate a driving voltage for the actual temperature changes in the four regions.
In order to solve the foregoing problem, Japanese Laid-Open Patent Application publication No. 81607/2000(Tokukai 2000-81607; published on Mar. 21, 2000) discloses a liquid crystal display device including (i) temperature sensors 202a to 202d provided at the edges of a liquid crystal panel 201, and (ii) at least one temperature sensor 203 for measuring temperature of a display region in the liquid crystal panel 201. In the foregoing liquid crystal display device, temperatures in respective predetermined pixel regions in the liquid crystal panel 201 are estimated based on temperatures measured by the temperature sensor 203 and the temperature sensors 202a to 202d. Then, for the predetermined respective pixel regions, actual intensities of image data signals are corrected in accordance with the estimated temperatures of each of the predetermined pixel regions, so that the actual intensities respectively become target intensities that are set for prescribed temperatures of the liquid crystal display panel 201. Then, in accordance with the image data signals thus corrected, signal voltage is generated.
As described, by providing at least one temperature sensor 203 in the display region in the liquid crystal panel 201, the brightness of the liquid crystal panel 201 is corrected individually with respect to each of the predetermined pixel regions. As such, even if there is fluctuation in temperature distribution in the liquid crystal panel 201, it is possible to constantly maintain a good brightness of an entire displaying surface of the liquid crystal panel 201 at the predetermined temperature. As a result, in the foregoing liquid crystal display device, the image data signal for the liquid crystal panel can be controlled, regardless of whether or not there is a change in the temperature of the displaying surface of the liquid crystal panel.
However, in the liquid crystal display device disclosed in the foregoing Tokukai 2000-81607, it appears that the temperature sensor 203 at a center of the liquid crystal panel 201 is actually a thermoelectric couple provided at a back side of the liquid crystal panel. This is because the thermo sensor 203 cannot be provided on a surface of the liquid crystal panel 201 lest image displaying be disturbed by the thermo sensor 203 provided on the surface.
Since actual temperature of a displaying element is not measured in the foregoing Tokukai 2000-81607 either, it is only possible that the pulse widths of the scan voltage and the signal voltage are changed in accordance with an approximate temperature estimated based on the estimated temperature.
In overshoot method, because the response speeds for respective pixels are improved, it is important for the control of the correction voltage to keep the liquid crystal elements within a specific temperature range. Therefore, the aforementioned drawback is an important problem in the overshoot method.
Furthermore, Japanese Unexamined Patent Application, Publication No. 4-318516/1992 (Tokukaihei 4-318516; published on Nov. 10, 1992) discloses a technology in which a temperature of a liquid crystal panel is measured, and data signals are emphasized in accordance with the temperature measured.
However, the response speed of the liquid crystal largely depends on temperature of the liquid crystal itself, and the response speed becomes dramatically slow at a low temperature of the liquid crystal. Further, more-than-necessary overshooting causes the liquid crystal to respond more than necessary. Such more-than-necessary response causes a displayed image to look unnatural. For this reason, it is necessary to adjust output level of the overshooting in accordance with the temperature of the liquid crystal.
Thus, gradation correcting data corresponding with a plural degrees of temperature are necessary for the liquid crystal display device. Further, alongside the development of larger liquid crystal display devices in recent years, the problem of the liquid crystal temperature unevenness (unevenness in the temperature of the liquid crystal) in the displaying section is becoming increasingly important. Conventionally, in the overshoot method for liquid crystal display devices, the output levels of the overshooting are adjusted, in group or as a whole, based on the temperatures at the edges of the liquid crystal panel, without considering the individual pixels. Especially, there is no attempt to perform correction to compensate for the temperature unevenness in the display region.
Furthermore, it is preferable that the liquid crystal display device be such that the line of the scan signal wiring are driven on a line-by line basis, whether or not the overshooting is carried out.